Myle's suggestion is the one id go with...
But for the record
To pull a value
myvariable = forms!thatformname!thatcontrolname
To push a value
forms!thatformname!thatvariable = thatvariable
You can do this in forms or reports
You can use controls, variables or objects on either side and you are not constrained to use on both sides. So you can set a control using a variable.